This invention relates to steam cookers, and in particular to a process for automatically deliming the cookers at predetermined intervals to avoid damage caused by lime deposits.
Commercial cooking ovens that use a steam generator are well known, as are ovens that use a combination of steam and convection air cycles. As water evaporates, however, lime scale deposits form on the surface of the steam generator and it is known to use a deliming solution to remove the scale. Such deposits are a major problem especially with commercial cookers because the deposits formed defeat the efficiency by interfering with heat exchange and with water flow or by disrupting the liquid level sensing system typical in such devices.
The oven operator must pour a deliming agent directly into the steam generator using an internally or externally mounted reservoir. This procedure is labor intensive and therefore often is not performed or performed infrequently resulting in damage to the steam generator.
In U.S. Pat. No. 5,152,252 there is described the use of a controller which controls both feed water input to a boiler and the addition of chemicals to that feed water. The chemicals are only added with the feed water so that if the flow of feed water stops the chemical application stops. The invention described, however, is directed to a large boiler such as one used to heat an office building and super heated water flows under pressure from the boiler to an appliance where the pressure is reduced to convert the water to steam. A separate feed water tank is provided outside of the boiler and condensate from the appliance or building is returned to that feed water tank for recycling. There is then no disclosure relative to a table top steam cooker wherein an internal water supply generates steam used to cook food.
In U.S. Pat. Nos. 5,193,491; 5,279,676; 5,368,008; and 5,640,946 a steamer apparatus is described wherein cleaning and deliming agents are introduced into the steam generator through the steam lines connecting the generator and the oven. This is done manually, however.
U.S. Pat. No. 5,193,491 describes a boiler separate from the cooking chamber and a reservoir for descaling solution all housed within a common cabinet. There is no disclosure of a steamer disposed within the cooking chamber and a remote reservoir and pump whereby heat problems from steam generated would not affect the reservoir. The reservoir is described as being constructed from an acid resistant polypropylene or other suitable plastic material. In U.S. Pat. No. 5,368,006 the deliming solution is added through a funnel into the steam inlay housing for manual introduction of the solution into the boiler. U.S. Pat. No. 5,279,676 is a division of U.S. Pat. No. 5,193,491 and therefore similarly disposes the identical unit. Finally, U.S. Pat. No. 5,640,946 is a division of U.S. Pat. No. 5,268,008 and therefore describes the same unit as is described in that patent.
Also, in U.S. Pat. Nos. 5,549,038 and 5,631,033 a sensor is used to activate a timing circuit to shut down the steamer when it is necessary to delime. The deliming process, however, is not automatic but the timer provides an indicator to the operator that the oven is ready to delime and since the steam generator is automatically shut down the deliming process occurs when necessary, but manually. In these patents a timing circuit is used with a preset timing period. The time necessary to heat water is measured and if it meets a predetermined period no indication is given. However, if the timed perod is excessive an indicator light is triggered. The operator can override the indicator light once. In a subsequent time if the time period is exceeded the steam generator circuit is disabled. Prior to disabling, however, the steam generator circuit will be allowed to increase the steam temperature to 193xc2x0 F. which the patent specification indicates accelerates the activity of deliming solutions. Subsequent to deliming, the heater is flushed with water to remove the deliming solution.
Finally, chemical dispensing systems are described in U.S. Pat. Nos. 5,564,595 and 6,236,321 wherein the dispensing of chemicals is controlled by a microprocessor. U.S. Pat. No. 6,236,321, however, describes use in a hot water heater not a steam generator, and uses a sensed increase in reheat time to initiate a clean out alert.
Accordingly there is a need for a process for not only notifying an operator when it is necessary to delime, but also for automatically deliming the steam generator in a commercial steamer oven with a minimal involvement by an operator so that the deliming process will proceed at an optimum time to maximize the overall efficiency of a steamer oven.
According to the process of this invention a microprocessor is used which controls a peristaltic pump, a cold water inlet fill-solenoid and a waste drain pump. The microprocessor also controls the user interface on the machine which includes a signal such as a light used to indicate to the operator when the deliming process is to proceed. The interval between deliming is based upon water hardness which in turn can be determined using well known publicly available data for a particular geographic area and not on a measure of the time necessary to reheat the water. The interval then is set with a potentiometer couple to the microprocessor.
The cooking device runs normally until the deliming day interval is reached and at this point an indicator lamp on the front panel flashes, prompting the operator to start the deliming process. At this point the operator may choose not to start the process and can continue using the oven. The operator can start the process at any time, most likely at the end of the day.
The operator then starts the deliming process by turning the appliance into the cool down, and pressing a button sending an input signal to the microprocessor controller.
The controller then sends the appliance into a non-cooking state and starts the deliming process by heating the steam generator to insure the water is above 180xc2x0 F. Then, a peristaltic pump is activated for a period of time pumping a predetermined amount of deliming agent from a reservoir external to the device into the steam generator. The controller then deactivates the pump and initiates a timer for the correct period of time to allow the deliming agent to work. The controller then empties the steam generator by running a discharge pump and adds a fresh water to rinse the steam generator through the fresh water solenoid after the rinse the steam generator is emptied by running the discharge pump and subsequently the appliance is reset to a cooking enabled state and the interval counter also is reset for the number of steam generator run hours to the next deliming process.
The microprocessor records the date of the deliming process in non-volatile RAM. The records stored in the non-volatile RAM can be accessed via a computer, or PDA using a serial data connection to the microprocessor, the microprocessor also records, the different steps of the deliming process into NVRAM. In case of a power fail, the microprocessor has battery backup, and will restart the deliming process where it left off before the power fail.
The process then involves only minor operator activity as the microprocessor controls the deliming process and when it is to be initiated.
Accordingly it is an object of this invention to provide an automatic deliming process using a microprocessor to control when the process is initiated and to control the actual deliming process itself.
It is another object of this invention to provide a timed deliming process for a commercial steam cooker wherein a controlled volume of deliming solution is automatically added to the steam generator during the deliming process, and removed after a pre-selected period of time so that the generator can be rinsed and reset to a cooking mode.
It is another object of this invention to provide a microprocessor for controlling the deliming process for a commercial steam cooker wherein the microprocessor controls a peristaltic pump for adding deliming solution to the steam generator, controls the discharge pump for removing the spent deliming solution from the generator, controls a fresh water inlet for rinsing the generator and further controls the pump for removing the rinse water.
These and other objects will become apparent with reference to the drawings and following description wherein: